The previous three essays suggest some important linkages between nation and regional economic development; the fourth essay attempts to explore these aspects in a more formal way by examining the path of regional income inequality in China. The fourth essay employed a non-parametric method to examine spatial effects modeling the regional income disparity pattern in China. The main findings are that with the enlarging regional income disparity between the core region (coast) and the periphery region (west), China's regional income distribution has moved from convergence to stratification and from the stratification to polarization. The trend of "high income regions remaining high" and "low income regions remaining low" will result in a long-lasting regional disparity between the core and the periphery regions.